Landslide prediction a risky venture: Who will move first, the hillside or the homeowner?

BEN LOMOND -- No one foresaw the collapsing hillside that killed 10 people along the Santa Cruz Mountains' Love Creek in 1982. Four people still lie buried there, never to be found.

But no one knows better than Santa Cruz geologist Gerald Weber that predicting landslides is a perilously imprecise science. Three decades later, with Washington state's tragic mudslide rekindling memories, Weber is still torn by a decision he made that changed so many lives.

Worried -- perhaps needlessly -- about the Love Creek hillside's continued threat to 28 families, officials ordered them to abandon and raze their beloved homes.

A generation later, despite rainy winters and the nearby Loma Prieta earthquake, the mountain slipped several more feet -- but then stopped.

A mangled retaining wall rests on one of four homes damaged by a landslide in Hercules, Calif. March 2011. (Bay Area News Group)
(
Dean Coppola
)

"They could have lived out their lives. People look at me and say, 'You ruined my life.' I stole their homes from them," Weber said.

"No one can tell when it will move again -- but when the whole thing comes down, it will be catastrophic," he said.

The Bay Area is replete with unstable hillsides that could instantly collapse during a heavy rain or an earthquake. But Love Creek's lesson is one of nature's utter unpredictability. Some hillsides, such as Berkeley's, creep slowly, moving a quarter to 1 ½ inches a year with no risk for people. Others stand steady for millennia.

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"Where? When? How big? Those are the three big questions we are trying to answer," said U.S. Geological Survey landslide expert Jonathan Stock, who is using probes to measure hillside moisture and slippage in east Castro Valley, Marin County's Lucas Valley, San Bruno and Pacifica's Montara Mountain.

Most of our pleated hillsides go unwatched, except for a few key sites, among them the East Bay's 2"'mile"'wide concentration of homes between Skyline Boulevard and Interstate 580.

Dramatic slippage, if seen in time, would trigger an alert. But it is tough to interpret subtle cracks, often concealed by vegetation, that signal trouble.

"You're damned if you do, damned if you don't," said 73-year-old Weber, an adviser to the Santa Cruz County Planning Department in the days following the Love Creek slide. "Landslides work on a geologic time scale -- over many human lifetimes, if not dozens, or hundreds. That's what makes it so difficult."

The night of Jan. 5, 1982, is seared in his memory. After two days of torrential El Niño rains, a large section of hillside above Love Creek, a tributary of the San Lorenzo River at Ben Lomond, crashed into the canyon below. Thirty homes were destroyed, and 10 people died.

As in many other steep, beautiful canyons in the Bay Area, Love Creek was the site of a previous landslide. In addition, residents had noted signs of shifting soils, such as falling redwood trees.

But the scope of the instantaneous collapse was stunning. Many other Bay Area mountain sides slumped during that same storm, when 19.7 inches of rain fell in one 30-hour period. A Pacifica slide killed three children. One in Tiburon killed a noted San Francisco State professor.

"I remember getting to the slide area and being simply aghast," Weber said. "Houses were essentially ripped apart and partially to almost totally buried. The slide mass was soaking wet in most places, oozing water; trees were lying around -- helter-skelter, crisscrossed ... you name it. The few people who survived it were in shock."

As excavations began, "I occasionally would see a family member sitting ... watching the backhoes dig into the debris piles ... waiting to see if they would find the body of a loved one," he said. "Pretty grim stuff."

It took 10 days to find the bodies of Lynda and John McCluskey, who worked the night shift at the Scotts Valley-based microwave communication system Watkins-Johnson.

Their two sons, Trevor, 7, and Kelly, 5, are still buried under a mountain of dirt.

Weber and other geologists then noticed a rupture at the top of an adjacent flank of the mountain. In the anxious months that followed, they watched it drop several feet on three different occasions. They concluded that 600,000 tons of soil and rock could slide in another saturating rain.

"I was faced with this incredible question: How bad is this continued risk?" Weber said. "I knew that if it slid, it could kill another 30 to 40 people.

"We built this house ourselves. We had a new baby, we lived in a trailer, we toughed it out," said Ron Heine, another resident.

For the next 15 years, residents fought back in court, unsuccessfully. Homeowners said they were threatened by Santa Cruz County bulldozers; geologists said their lives were threatened.

Eventually, the homes on Upper Way and Lower Way -- from beautiful new two-story structures to modest cabins -- were abandoned, then destroyed. The county did not compensate the families for their losses, and they had to tear down their houses to qualify for federal disaster aid. "If the government takes something for public purposes, they have to pay for it. If nature makes something you own uninhabitable, that's between you and God," said Santa Cruz land-use attorney Gary Patton.

Now the once-muddy graveyard is serene and forested. Along the steep flanks of the hill, flat benches of earth are the only clues to the old neighborhood.

Below, newly renovated houses cluster along Love Creek's canyon.

"It has already slid. That's what mountains do. It's fait accompli, no longer dangerous," said Michael Athan, who lives in a cabin on Love Creek Road near the old slide.

The Washington landslide -- which killed 36, with 10 still missing -- is rousing calls for review of laws to ensure that people aren't living or working downhill from disaster.

In most cases, unless there is imminent risk, communities are reluctant to deprive property owners of their right to build, said Patton, a Santa Cruz County supervisor at the time of the Love Creek disaster.

Aptos recently approved houses under an eroding coastal bluff. In the Berkeley hills, a 6,500-square-foot house is planned despite soil slippage nearby.

But California increasingly requires geologic review before construction, especially for properties in known slide zones. Sites deemed hazardous may require special engineering.

To offer more protection, geologic landslide detectives are working hard to improve slide prediction.

They've found that two conditions -- soaking rain and sedimentary geology -- conspire to cause a monster slide, said USGS' Stock.

When heavy rains saturate soil, water pressure builds between soil particles, pushing them apart, liquefying the soil that literally flows down the hillside.

Soil loosely layered in sediments can slip like a deck of cards. Previous slides on a site also enhance risk, because slipped soil is loosely deposited on the hillside. Earthquakes can trigger slides. A heavy rain, combined with a quake, would multiply them.

The government doesn't have the budget or technical capability to monitor every weak hillside. A slide hazard map of the Bay Area paints nearly every hillside bright red in warning.

Instead, the USGS has a patchwork of warning programs, monitoring rainfall and soil moisture and pressure measurements. The data can be used to estimate the likelihood of a slide in a large region during a big storm.

"But we can't tell you if one will land in your backyard," said Stock, director of the USGS Innovation Center for Earth Sciences.

Without such information, there's an imperfect balance between public safety and private property rights, experts said.

"It's like playing God," Weber said. "You're just trying to do more good than harm, in the long run."

Contact Lisa M. Krieger at 650-492-4098.

LANDSLIDE WARNING SYSTEM?

Landslides are difficult to predict because they occur:

-- Sporadically, over hundreds or thousands of years. -- Across a broad landscape, often very remote.-- With warning clues going unnoticed because some fractures are underground or hidden in vegetation.

But there are new efforts to detect ground movement using different techniques.

-- Radar waves, reflected off the ground, can detect minute shifts in distance between a satellite and the ground, revealing earth movement. -- Shifts in the pixels of digital photos of landscapes can reveal subtle movement. -- Both techniques require vast amounts of data collection -- and someone trained to interpret the data and alert authorities to sudden changes.

THE LOVE CREEK SLIDE

An aerial view showing the extent of the 1982 disaster the day after it occurred is at http://bit.ly/1nebJW1.